Adsorbent particles with nanometer-size pores (nanoporous particles) like metal-organic framework (MOF) materials, exhibit a capacity to store hydrogen at cryogenic temperatures and moderate pressures (e.g., 20 bar). Members of this family of materials have pore sizes in the mesoporous range (greater than twenty angstroms) and low densities for crystalline materials. Metal-organic framework materials are often characterized by metal-oxygen clusters connected by molecular struts such as multifunctional organic moieties. For example, zinc-oxygen clusters may be connected in a three dimensional network with 1,4-benzenedicarboxylate groups (available as MOF-5). Such crystalline materials usually don't have molecular walls that impede diffusion of guest molecules such as hydrogen. The pore size of the metal-organic framework materials may be varied by selection of the wire-like molecules interconnecting the metal-oxide clusters.
Hydrogen gas under pressure and at a suitably cold temperature may be brought into contact with the adsorptive particles and stored under pressure in the porous material. The hydrogen storage may be maintained at a suitable storage temperature and pressure until there is a need to withdraw hydrogen for a fuel cell or other hydrogen-consuming power plant or device. Such an adsorption-desorption process is reversible.
Metal-organic framework materials and other solid adsorbents thus provide a basis for on-board storage of hydrogen at temperatures at or below that of liquid nitrogen (about 80K) and pressures of about 20 bar. A volume of adsorbent particles contained in a vessel adapted to maintain the specified temperature and pressure of the hydrogen-containing material would provide the basis for a fuel tank for a vehicle. The tank would have openings for storage and withdrawal of hydrogen.
Hydrogen could be made available at fixed, geographically located “hydrogen stations” in the form of compressed hydrogen gas (CGH2) or as liquid hydrogen (LH2). Hydrogen gas would then be prepared at the hydrogen-fuel station for passage into contact with the adsorptive contents of a hydrogen-fuel tank of a vehicle brought to the station for re-fueling. Desirably, the hydrogen is passed into contact with the adsorbent particles at pressure and temperature conditions that permit rapid refilling of the adsorbent materials and that can be readily attained at the fuel station.